Method of treating metals, such as steel or steel alloys.



C. J.'GRIST. METHOD 0F TREATING METALS,SUCH AS STEEL 0B. STEEL ALLOYS.

APPLIUATION FILED 131102490?I 91 6,302. Patented Mar. 23, 1909.

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U'Nirn smilies PATENT orricn.

CHARLES JAMES GRIST, OF LONDON, ENGLAND.

METHOD 0F TBEATING METALS, SUCH' AS STEEL 0R STEEL ALLOYS.

Patented March 23, 1909.

Application tiled December 2, 1907. Serial No. 404,788.

To ail whom it may concern:

Be it known that I, CHARLES J AMES GRrsT, a .subject of the Kin ofGreat Britain, residing at 24 Rood ane Chambers, in the city 0f LondonfEngland, metallur ist, have invented certain new and useful mprovetnents'in Methods of Treating Metals, such as Steel or Steel Alloys, of which the following is a speciflcation.

This invention relates to e process for improving the quality of steel which consists in heating it in a hath of mercur and pass ing an electric current through tie material while at arecalescent period during the heating or cooling. y .The invention is based on the discovery that peculiar advantages are to be attained by passing the current at certain selected portions of the time temperature curve during the heating or cooling, or both which are h eginafter referred to as recalescent pe- 1-1 s.

It is Well known to metallurgists that if a piece of steel lie-subjected to a uniform and constant supply of heat the curve which represents the tune rate rise of temperature is not uniform. lherc are certain )oints on thil temperature curve (known as tlm re ralescent or critical points or eriods) when the rise in tem erature is sud enly arrested` or retarded Wit or Without fluctuations; after this has occurred the uniform rise in teniperature is resumed. v Vhile the metal is cooling similar recalescent points or periods occur at. which the fall in temperature is a rrested or retarded although the reculescent points during a falling temperature do not usually exactly coincide on the temperatture curve with those of a rising temperature. The temperature curves about the recalescent periods Will present irre ulnrities, although the outsidesource of eat is uniform. Marked recalescent periods have been observed between 500o (l. and 1,009" C.. but it is possible that therenre other reralescent periods which present th'.l salue phenomena. and are similarly suitable to the purpose of this invention. Chill hardened steels as well es very low grade steels present recalesoent periods as 10W as 200n to 400o C., which periods may be utilized. In

noch case a. recalescent period must. beascertained. Di [ferent steels present different ret-alesceut periods and no one formula will serve l'or nil.

The invention consists in passing the electric current through the nuiteriel during these lecalcscent periods only, as cxplained, the recalescent periods of the as cending and descending time temperature curvesv being first selected, and the current being passed preferably during the whole of either or both of such periods in the present specification. By the terin "recalescent, a certain period in the ascending, and a certain period in the descending time temperature curves is included. Recalescent points are ascertained by any well known method, such for example as that followed by Mons. Le Chatelier who used a thermo-electric pyrometer. Results will be found to vary accordingr to the particular recalescentperiod selected during which to pass the electric currentv Results also vary according as the recalca-)rent periods are se lected on the rising or falling temperature curve. According to the variety of metal treated, it is generally found most advantageous to select that recalescent period for steel which is most. marked. When the process is carried out u on any steel which lms been tempered "f a ter hardening` such steel should not be heated up to the teniperature at which it was "tempel-ed.` When the steel has been only hardened end not tempered the temperature of the steel when reheated must not be allowed to rise .dened unless it be decided to continue thi-l process over the next recalesrent period.' Having Satisfied oneself as to a suitable reralesront period. a suitable voltage of current to produce the best results is next as cci-tained. As a` general rule a goed z', c. a well manufactured, close or homogeneous stool will require a higher voltage than zt bad i. e.-an ill-manufactured. loose or irregular steel. At the some time it must be born-e in mind that the richer a steel is in carbon` or alloyod metals. the higher nust be the voltage and it is found that a g( ed stewl with a high percentage of carbon will require (say) a current of 200 to 500 volts; whereas a had steel with n high percentage of carbon could be effectively treated. at from 50 to 200 volts: and lastly a bad" termined and this wil be found to vary to the temperature at which it was har? steel with a Vlow percentage of carbon would with the matehal to be treated, the apparatus and the mercury or mercury vapor I therein. ln the apparatus described hereinafter (for treatment of small tools and test pieces) a current of from 15 to 25 amperes is used. The quantity of mercury sur l rounding the steel has to be considered and I for the work instanced the tank is so arranged as to surround the steel with from l to -1 inch of mercury. By reason of the large capital expenditure, which operations on large pieces for experimental work would necessitate only small tools and pieces of steel have u to the present been 'dealt with, but this mvention is also applicable to the treatment of large pieces.

| l l Referring to the accompanyirw drawings l which approximately indicate tie disposii tion of the parts of an apparatus designed to carry out this invention, A is a` circular wrought iron tank provided with an iron flange B. It is important in all cases that this tank should be of as small capacity as possible consistent with the size of the pieces of metal to be treated. The cover E is provided with au annular llange l to it into a i corresponding slot Q in the flange B, the slot being packed with asbestos to form a tight l joint; F, F are the bolts which hold down the lid E to make the joint; a hollow piece of steel I passes throughta hole in the lid and is electrically insulated therefrom by asbestos or other suitable packing' O, I). J l

This hollow piece ot steel l is proided with a clamping screw H, and serres as a holder for the pieces of steel M, which is beingr treated and the other end of which is in contact with the bottom of the tank. The nut 'l is used for screwing up and makin(Jr a joint with asbestos O, between the hol low' iiecel l and the lid E. The pyrometer couple J is inserted in the top of the hollow piece l. The tank A is surrounded by an inner mullle (l lined with ircbrick standing on legs V ..V, these parts beingr insulated thermallv with asbestos sheet 03, O, which support the whole ap aratus and an outer mutlle I) lined with as )estos 0' to minimize i l the loss of heat.

The whole apparatus is surrounded by a casing (i llned with asbest-os or other heat insulating material O2.

The tank A contains the requisite quantity of mercury or mercury Vapor N, Y. The temperature is raised means ot' gas jets H and the heated pro lucts of combustion pass .away in the direction of the arrows` over the inner inutile at R, R. The pyrometer connected to the couple J b the wires L is watched. When the reca escent oint is reached electric contact is establisied (in the arrangement illustrated) through the holder I as the negative pole and a current i of electricity is passed as for instance through the connections Y, Z. It is assumed thata suitable electric resist-ance will be inserted in the circuit between the apparatus and the source of electric energy. f

This invention results in toughening and thereby increasing the life and etliciency ot tools and other articles submitted to this treatment.

1. A method of treating metals which cousists in heating the metal to afrecalescent period' in the presence of mercury and at a recalesccnt period passing an electric current` through the metal. A

2. A method of treating metals which consists` in heating the metal beyond a recalescent period and allowing it to cool in the presence ot' mercury, and passing an electric current through the metal during the re4- r'alescent periods on 'the ascending and descending time temperature curves.

P. The herein described improvement in the treatment ol metals which consists in passing an electric current through the metal while the same is heated to a recalescent point in the presence of mercury.

In testimony whereof I have hereunto set my hand in presence ot two subscrlblng w1tni-sses.

CHARLES JAMES GRIST. W it nesses z t HAuoLn Hanni' YAmoo'r'r,

(ino. J. Il. FRANKLIN. 

